A light-emitting diode (LED) is generally formed of a first contact layer, an active layer, and a second contact layer that form a diode that will generate light when it is forward-biased. When generated, this light will generally propagate outwards in all directions from the active layer. In most cases, however, it is desired to direct the light in a very specific direction, which, without any type of reflector, would only receive a small portion of the total light emitted by the LED. Additionally, if the LED is formed on a light-absorbing substrate such as silicon, the light that propagates towards the substrate may be absorbed by the substrate and be mostly lost rather than merely going in an undesired direction. Generally, when this occurs, less than about 10% of the light would get reflected when the light impacts a silicon substrate.
To combat these problems, reflectors have been formed as part of the LED in order to direct the light in a desired direction and away from any light-absorbing substrates. One typical reflector is a distributed Bragg reflector (DBR), which uses alternating layers of materials having different refractive indices to reflect the emitted light. While a DBR is helpful, however, it is not omnidirectional, as the reflectivity of the DBR drops when the angle of incidence of the light impacting the DBR increases relative to normal to the surface of the DBR. This drop in the efficiency of the DBR causes a corresponding drop in efficiency of the LED.
Accordingly, what is needed is a reflector that has a greater efficiency for a larger range of incident angles.